new light on old sites

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Geophysics Methodology 101 – Part One

There were two major questions we needed to consider when it came to tackling geophysics for Swallowcliffe:

  1. How do you pick a place to do geophysics?
  2. How do you actually do geophysics?

We’ll walk through each of these questions and really break them down.

Question #1 – How do you pick a place to do geophysics?

As you can see from our previous post on the site’s location, the area we’re looking at is pretty large. English Heritage scheduled an area covering three separate fields:

Swallowcliffe_Down_1945_Field names

Dr. Clay’s 1920s excavation of Swallowcliffe Down took place in an area that overlaps Fields B and C, and parts of Field A were also mapped and possibly explored (the original excavation can be quite unclear sometimes!). When Elizabeth and I made our initial site visit in Spring 2014, we found visual evidence of the site in the lower right-hand corner of Field B:


It’s difficult to see, but there’s a slight, semi-circular ridge a few meters beyond the fenceline. English Heritage also recorded a series of undated dyke systems at the opposite end of Field B. We also found a raised earthwork in the upper right-hand corner of Field A:


For these reasons, we decided to prioritize the lower right-hand corner of Field B, all of Field C, and as much of Field A as possible (focusing on the upper right-hand corner). We wanted to survey the dyke systems on the left-hand side of Field B as well, but there were several issues with that:


We’ll come back to this grid in Question #2, but for now, I would like to point out that each yellow square in the photo above corresponds to a 30 by 30 meter grid square. Therefore, Field B covers an area of about 93,600 square meters. Our team would only consist of six members working two machines in teams of three, and we would only have a week to complete the geophysical survey.

This is why we had to prioritize the specific areas that were mapped in Dr. Clay’s original report (the areas marked in red). We promised ourselves we would survey as much of the center and left side of Field B as possible, depending on how quickly we would get through the area of the site itself and how the data looked. While it would be great to find new things outside the site, we wanted to find the things Dr. Clay missed within the site – specifically, Iron Age roundhouses and four-post structures.

So, now you know how we picked the site. Coming up next: how to do geophysics!


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Brief Introduction to the Project

Hi there!

Our first post contained an excerpt from our funding application, but I thought I would provide a better explanation of our project and why it is significant.

The site at Swallowcliffe Down in Wiltshire was excavated in the 1920s. An interesting array of material was recovered, including pottery, spindle whorls, weaving combs, glass beads, and brooches. This material came from a series of pits that Clay excavated. In the 1920s, they though that people in the Iron Age lived in the pits and that they represent the domestic structure of time time. Now we know that this wasn’t the case and that the pits were most likely used for grain storage. However, because of Clay’s excavation methodology (which is very different from today’s), he did not look for other structures, such as roundhouses.

Our project aims to re-explore the site at Swallowcliffe in an effort to better understand the nature of the site. We are using geophysical survey to locate the original excavations, but we are also hoping that we will be able to discover new previously unknown features. The nature of the site remains very unclear, since we cannot definitively say whether it was a settlement or not, without evidence for roundhouses. There is also quite a lot of evidence for other periods of activity at the site, so it will be interesting to see how the Iron Age site relates to earlier features and how later activity relates to the Iron Age site.

We hope that this provides a useful overview. We will be updating the blog and twitter account throughout the fieldwork from the 19th-24th of July.